I have now been through 4 ac blower speed switches (and of course you have to buy the entire HVAC unit). The plastic internals of the switches keep melting to the point that the contacts shift and the switch is damaged beyond repair. I have tried replacing the blower fan however this last switch melted no longer then 2 months after swapping out the blower. I didnt think the resistor would be at fault because if that isnt working right it still shouldnt put out more then the highest speed voltage, am I wrong with that? Also this time I havent been using the highest speed (4) just in case, but today it melted position 3, the rest still work but obviously there is still an issue. Please if anyone has any idea what could be causing this let me know, I have already spent over $400 trying to fix this...

Wow, it gets hot enough and the plastic looks like it boils, I could see it causing a fire which is not good! Living in Arizona AC is essential though. They need to do something about this if it is that common of a problem! I am sick of buying these switches when they just keep melting, what a poorly made switch too...

The problem is with the wiring that jeep uses, to small of a gauge wire for the job. The blower motor bushings wear out in time, causing the motor to pull more current than the switch can handle. (Melted switches and wires) Adding a relay between the switch and the blower motor resistor WILL fix the problem. Mine started with the third speed setting and moved up to the fourth setting. I added two relays, one for each of the highest settings. This is how you can fix it once and for all.

The wire for the 3rd fan speed is light blue on my '01 TJ. I cut this wire just past the switch. I extended the switch side of the light blue wire with a short piece of 12 gauge wire which I connected to terminal 85 of the relay, this provides the signal to energize the relay. The other side of this wire goes to the resistor block, I extended it with a short piece of 12 gauge wire that I connected to terminal 30 of the relay, when the relay energizes a ground will be applied to the resistor block through the light blue wire. 12 volts is needed for the relay to energize, I got this from a 12 gauge wire that I ran straight to the battery and connected to terminal 86 of the relay. I've connected a long piece of 12 gauge wire to terminal 87 of the relay, this will get attached to a good ground somewhere under the dash. That should complete the installation. I've burned out position 3 on the switch twice and I hope this will prevent that ever happening again. I may even go ahead and throw a relay on position 4 as well. Positions 1 & 2 don't see as much current as either 3 or 4 and should be fine without the mod.

Thanks for the info JBTJ, mine is a 01 too but my wires are always fine, just the plastic in the switch melts in no time. I just replaced the blower motor with a brand new one so it shouldnt be pulling more power then normal. Nice schematic there but I dont think I am good enough at electronics to follow that...

yeah thats the right way! but i dont have the time to do all that. so i bought the switch, some connectors, cut the pignose out of the harness, spliced it in... and tell my passengers that if they put it on the highest setting they may kill us all with a fiery death!

There used to be the website that described how to fix the bad ground problem with the system, but it appears the website is no longer up. If you use the relays described in the above link you shouldn't have anymore problems.

My blower fan switch seems to be on it's way out too. Yesterday in the afternoon the fan would not work at all. Both fuses are OK, and the blower motor resistor is brand new. This morning, the fan works fine on all speeds. This is the second time it's done this. I guess it's a warning! I ordered a new switch from Morris 4x4 to have on hand. It was only $21 delivered. Looks like I have a little project for next weekend already!